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Optimum Aspect Ratio for a Fermenter

What is the optimum aspect ratio (or height/diameter ratio) is for a fermenter?   The best answer is “it depends”. There is simply no universal optimum. The best design is worked on a case-by-case basis. We can list some factors that affect the optimum. Note that as aspect ratio increases, the following results are produced:

  • The vessel cost usually increases, except at the transition between shop fabricated and field fabricated vessels;
  • The total power (agitator + compressor) decreases at constant mass transfer rate;
  • The available heat transfer area increases;
  • The blend time is longer;
  • The composition is less uniform, especially DO;
  • The agitator gear drive becomes less expensive as there is less torque;
  • More impellers are needed; and
  • The shaft design often becomes more challenging.

These are but a few of the factors affecting the optimum aspect ratio.  Some factors will favor a taller aspect ratio, while others will favor a shorter ratio.  At Lee Enterprises Consulting, we have a number of highly qualified agitation experts available to assist you with any related matters.  Feel free to call or email us for more information.